1. Field of the Invention
The present invention relates to a thin and lightweight semiconductor device and a method of fabricating the same.
2. Description of the Related Art
In recent years, flat panel displays such as liquid crystal displays or organic EL displays have been used as a display device of a portable information device such as a mobile phone or PDA or a mobile personal computer.
Such a display device detects the surrounding luminance with an optical sensor, and controls the luminance to be displayed on the display device. By detecting the surrounding luminance in this way to obtain appropriate luminance to be displayed on the display device, wasteful power consumption can be reduced.
An optical sensor is made mainly of a semiconductor, and a typical example of the semiconductor material is silicon. Optical sensors formed using silicon are divided into sensors made of single-crystalline silicon or polysilicon and sensors made of amorphous silicon. An optical sensor made of single-crystalline silicon or polysilicon has the highest sensitivity to light in the infrared region of around 800 nm, and is sensitive to light with a wavelength of up to around 1100 nm. On the other hand, an optical sensor made of amorphous silicon has little sensitivity to light in the infrared region and has the highest sensitivity to light with a wavelength of around 500 to 600 nm which are the central wavelengths of the visible region. That is, an optical sensor made of amorphous silicon has sensing properties close to the human visual sensitivity.
Such an optical sensor is generally in the form of a chip formed by integrating a sensor element and an output amplifier circuit constructed from thin film transistors over an insulating substrate, and is mounted on a wiring board.
With a reduction in size of portable information devices, there has also been a demand for a reduction in thickness and weight of a device like an optical sensor mounted on a wiring board. In order to meet such demand, a sensor element formed using a thin insulating substrate has been developed, for example (e.g., see Reference 1: Japanese Published Patent Application No. 2005-175436).